System and method for detecting a device requiring power

ABSTRACT

A system and technique for detecting a device that requires power is implemented with a power detection station. The power detection system includes a detector having an output and a return which are coupled together by the device when the device requires power. The detector includes a word generator for generating test pulses for transmission to the device via the detector output, and a comparator for comparing the detector output with the detector return. The power detection station has a wide variety of applications, including by way of example, a switch or hub.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. §119(e) toco-pending U.S. Provisional Application No. 60/148,363 filed on Aug. 11,1999, the contents of which are expressly incorporated herein byreference as though set forth in full.

FIELD OF THE INVENTION

The present invention relates generally to telecommunications systems,and more particularly, to systems and techniques for detecting a devicethat requires power.

BACKGROUND OF THE INVENTION

Data terminal equipment (DTE) devices are well known. Examples of DTEdevices include any kind of computer, such as notebooks, servers, andlaptops; smart VCRs, refrigerators, or any household equipment thatcould become a smart device; IP telephones, fax machines, modems,televisions, stereos, hand-held devices, or any other conventionalequipment requiring power. Heretofore, DTE devices have generallyrequired external power from an AC power source. This methodologysuffers from a number of drawbacks including interoperability duringpower shortages or failure of the external power source. Accordingly, itwould be desirable to implement a system where the DTE power is drawndirectly from the transmission line. This approach, however, wouldrequire a technique for detecting whether a DTE is connected to thetransmission line and whether the DTE requires power.

SUMMARY OF THE INVENTION

In one aspect of the present invention, a power detection systemincludes a detector having an output and a return, and a device toselectively couple the detector output to the detector return when thedevice requires power.

In another aspect of the present invention, a detector having an outputand a return includes a word generator coupled to the detector output,and a comparator to compare the detector output with the detectorreturn.

In yet another aspect of the present invention, a method for detecting adevice requiring power includes transmitting a pulse to the device,receiving the pulse from the device, and detecting whether the devicerequires power in response to the received pulse.

In yet still another aspect of the present invention, a transmissionsystem includes a transmission line interface having at least one port,a two-way transmission line coupled to one of the ports, and a devicecoupled to the differential transmission line, the device selectivelycoupling the two-way transmission line together when the device requirespower.

It is understood that other embodiments of the present invention willbecome readily apparent to those skilled in the art from the followingdetailed description, wherein it is shown and described only embodimentsof the invention by way of illustration of the best modes contemplatedfor carrying out the invention. As will be realized, the invention iscapable of other and different embodiments and its several details arecapable of modification in various other respects, all without departingfrom the spirit and scope of the present invention. Accordingly, thedrawings and detailed description are to be regarded as illustrative innature and not as restrictive.

DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood with regard to the followingdescription, appended claims, and accompanying drawings where:

FIG. 1 shows an exemplary embodiment of the present invention with adetecting station connected to a DTE via a two-way transmission line.

FIG. 2 shows an exemplary embodiment of this application with a FastEthernet switch having eight detecting stations.

FIG. 3 shows a detecting station connected to a DTE, the DTE beingmodified to include a low-pass filter.

FIG. 5 shows the logic that generates the test pulses and compares thetest pulses with the received pulses.

FIG. 4 shows a detecting station subsection and DTE requiring power.

FIG. 6 shows an exemplary embodiment of the low-pass filter.

FIG. 7 shows the sequence for DPM detection combined withAuto-Negotiation in a basic embodiment of the invention.

FIG. 8 is a flowchart that shows the sequence for DPM detection combinedwith Auto-Negotiation in a preferred embodiment of the invention.

DETAILED DESCRIPTION

In accordance with a preferred embodiment of the present invention, adetector is utilized to detect the presence of device on a transmissionline and whether the device requires power. The device can be dataterminal equipment (DTE) or any other device that may require power.Exemplary DTE equipment includes any kind of computer, such asnotebooks, servers, and laptops; smart VCRs, refrigerators, or anyhousehold equipment that could become a smart device; IP telephones, faxmachines, modems, televisions, stereos, hand-held devices, or any otherconventional equipment requiring power. If the presence of a DTErequiring power is detected, then the detector can supply power to theDTE.

The described embodiment has broad applications. For example, a numberof areas can benefit from power delivery over a transmission lineincluding IP Telephony, Web Cameras, Wireless Access Points, IndustrialAutomation, Home Automation, Security Access Control and MonitoringSystems, Point of Sale Terminals, Lighting Control, Gaming andEntertainment Equipment, Building Management, and any other area wherepower is required.

An exemplary embodiment of the present invention is shown in FIG. 1 witha detecting station 10 connected to a DTE 20 via a two-way transmissionline (detector output 30 and detector return 32). The detecting stationincludes a detector 12, a controller 14, and a power source 16. Thedetector 12 provides a direct interface to the DTE. The controller 14initiates control and the detection process. In the preferred embodimentof the invention, the detector is a physical layer transceiver (PHY)with detecting capability. The controller 14 causes the detector 12 todetect whether the DTE 20 is connected to the transmission line andwhether the DTE 20 requires power. If the Detector 12 determines that aDTE 20 requiring power is connected to the transmission line, it signalsthe controller 14. In response, the controller 14 activates the powersource 16, thereby providing power to the DTE 20.

The DTE includes a relay 22 connected across the two-way transmissionline 30, 32. The switches 22 a, 22 b are used to selectively connect thedetector output 30 to the detector return 32 in the power requirementdetection mode, and to connect the two-way transmission line 30, 32 toDTE circuitry 28 once power is applied to the DTE 20. Those skilled inthe art will appreciate that other devices can be used to selectivelyconnect the detector output 30 to the detector return 32 such aselectronic switches and other conventional devices.

In operation, the detector 12 determines whether the connected DTE 20requires power by sending test pulses to the DTE 20. In the default mode(power requirement detection mode), the relay 22 is de-energize causingthe detector output 30 to be connected to the detector return 32 throughthe relay switches 22 a, 22 b. Thus, any test pulses sent from thedetector 10 to the DTE 20 are looped back to the detector 12. Thedetector 12 determines that the DTE requires power if the test pulsesare looped back from the DTE 20 to the detector 10. When the detector 12determines that the DTE 20 requires power, it signals the controller 14.The controller 14 activates the power source 16, thereby deliveringpower over the two-way transmission line 30, 32. Once power is appliedto the two-way transmission line 30, 32, the relay 22 is energizedcausing the relay switches 22 a, 22 b to connect the two-waytransmission line 30, 32 to the DTE circuitry 28.

The described embodiment of the detector has a wide range ofapplication. For example, the detector could be integrated into atransmission line interface, such as a switch or hub, which linksvarious DTEs onto a local area network (LAN). This application wouldprovide a technique for detecting which DTEs, if any, connected to LANrequire power, and providing power over the LAN to those DTE's thatrequire it. FIG. 2 shows an exemplary embodiment of this applicationwith a Fast Ethernet switch 51 having eight detecting stations 40, 42,44, 46, 48, 50, 52, 54. Each detecting station includes a full-duplex10/100BASE-TX/FX transceiver (not shown). Each transceiver performs allof the Physical layer interface functions for 10BASE-T Ethernet on CAT3, 4 or 5 unshielded twisted pair (UTP) cable and 100BASE-TX FastEthernet on CAT 5 UTP cable. 100BASE-FX can be supported at the outputof each detecting station through the use of external fiber-optictransceivers.

The detecting stations 40, 42, 44, 46, 48, 50, 52, 54 are connected to adata bus 58. A CPU 60 controls the communication between detectingstations by controlling which detecting stations have access to the databus 58. Each detecting station has a detector that can be connected to aDTE. In the described embodiment, the detecting stations 40, 42 are notconnected to any device. The detecting stations 44, 48 are connected toIP telephones 62, 64. The detecting stations 46, 50, 52 are connected tocomputers 66, 68, 70. The detecting station 54 is connected to a faxmachine 72.

In the default mode, each detector of each detecting station sends testpulses to its respective device. Each detector would then wait to see ifthe test pulses from its respective DTE device is looped back. In thedescribed embodiment, if the IP telephones 62, 64 are the only devicesrequiring power, then the test pulses will only be looped back to thedetecting stations 44, 48. The detecting stations 44, 48 will thendeliver power to their respective IP telephones over the transmissionline. The computers 66, 68, 70 and the fax machine 72 do not requirepower, and therefore, will not loop back the test pulses to theirrespective detectors. As a result, the detecting stations 46, 50, 52, 54will not deliver power over the transmission line.

Although the detector is described in the context of a Fast Ethernetswitch, those skilled in the art will appreciate that the detector islikewise suitable for various other applications. Accordingly, thedescribed exemplary application of the detector is by way of exampleonly and not by way of limitation.

In the context of a Fast Ethernet switch, it is desirable to configurethe detectors to prevent failures of DTE devices in the event that thesystem is wired incorrectly. For example, in the Fast Ethernet switchapplication shown in FIG. 2, one skilled in the art could readilyrecognize that the computer 68, which does not require power, could beinadvertently wired directly to the IP telephone 64. If the IP telephone64 required power, a switch (see FIG. 1) would connect the two-waytransmission line together in the default mode. As a result, thecomputer 68 would attempt to negotiate data rates with the IP telephone64 on power up. The data rate negotiation in the described exemplaryapplication is governed by IEEE 802.3u Clause-28 rules, the contents ofwhich are expressly incorporated herein by reference as though set forthin full. This standard dictates an Auto-Negotiation methodology whereinFast Link Pulses (FLP) having a 100 ns pulse width are transmittedbetween devices. Accordingly, the FLPs transmitted by the computer 68would be looped back to the computer 68 through the relay contacts inthe IP telephone 64 (see FIG. 1). The computer 68 would interpret theselooped back FLPs as data from a device attempting to negotiate a datarate with it. The computer 68 would thus be unable to successfullynegotiate a data rate and enter into a continuous loop.

To avoid this potential problem, an exemplary embodiment of the presentinvention utilizes a filter in the front end of the DTE. Turning to FIG.3, a detecting station 10 is shown connected to a DTE 20′. The detectingstation 10 is identical to that described with reference to FIG. 1.However, the DTE 20′ has been modified to include a low-pass filter 34connected between the detector output 30 and the detector return 32through the relay switches 22 a, 22 b when the relay 22 is de-energize.The cutoff frequency of the low-pass filter 34 is set to filter out the100 ns FLPs. Thus, in this embodiment, the detector uses test pulseshaving pulse widths greater than 100 ns which will pass through thelow-pass filter. With this approach, if the computer 68 (see FIG. 2)were inadvertently connected to the IP telephone 64, the 100 ns FLP'stransmitted from the computer 68 to the IP telephone 64 would befiltered out by the low-pass filter 34 (see FIG. 3) thereby preventingthe computer 68 from entering into a continuous loop. If the system werewired correctly, however, test pulses wide enough to pass the low-passfilter 34 would be looped backed through the DTE 20′ to the detectingstation 10 indicating a requirement for power.

In operation, the detector 10 determines whether the connected DTE 20′requires power by sending test pulses to the DTE 20′. Typically, a 150ns wide pulse can be used, although those skilled in the art willreadily appreciate that the filter can be designed to pass test pulsesof any width. Preferably, the pulse width of the test pulses isprogrammable. The skilled artisan will also recognize that either asingle test pulse or a series of test pulses can be used to detect DTEsrequiring power. In the context of a Fast Ethernet switch, economydictates that a 16 bit word conforming to the IEEE 802.3 standards isused. This standard is already supported in the detector 12 andcontroller 14, and therefore, lends way to easy integration of the testspulses into the detector 10 without any significant increase incomplexity.

In the default mode (power requirement detection mode), the relay 22 isde-energize causing the detector output 30 to be connected to thedetector return 32 through the relay switches 22 a, 22 b. Thus, any testpulses sent from the detector 10 to the DTE 20′ are looped back to thedetector 10 through the filter 34. The detector 12 determines that theDTE requires power if the test pulses are looped back from the DTE 20′to the detector 10. When the detector 12 determines that the DTE 20′requires power, it signals the controller 12. The controller 12activates the power source 16, thereby delivering power over the two-waytransmission line 30, 32. Once power is applied to the two-waytransmission line 30, 32, the relay 22 is energized causing the relayswitches 22 a, 22 b to connect the two-way transmission line 30, 32 tothe DTE circuitry 28.

The 16-bit word generated by the test pulses can be a pseudo random wordin the described exemplary embodiment. This approach will significantlyreduce the risk that two detectors in the Fast Ethernet switchinadvertently wired together will attempt to power one another. If thisinadvertent miswiring were to occur, the chances that the detectorswould generate the same 16 bit word such that it would appear at eachdetector as if their respective test pulses were being looped back is½¹⁶. Alternatively, the 16 bit word could be an identifier such as acontroller address. In other words, the address would be embedded intothe 16 bit word. As a result, if two detectors were inadvertently wiredtogether, the exchange of test pulses between them would not be mistakenas a looped back condition because the controller address of eachdetectiing station is different.

To further reduce the risk of one detector mistaking another detectorfor a DTE, the detector could generate a narrow window in time when itexpects to receive test pulsed back after transmission. Thus, unless thetwo detectors are sending test pulses at or near the same time, a loopedback condition would not be detected. For example, using the IEEE 802.3standard, a 16 bit word is transmitted every 8 ms minimum. If the windowis set for the worst case round trip delay of each test pulse say 4 us,then the probability that the other detector would transmit its testpulses in the window is 1/2000.

Further reliability can be achieved by sending two groups of testpulses. The first group of test pulses will have sufficiently wide pulsewidths such that they pass through the filter of the DTE. The secondgroup of test pulses will be FLPs of 100 ns width as specified in theIEEE 802.3u Clause-28 rules. As a result, only the first group of testpulses will be routed back to the detector. The detector detects thefirst group of pulses and signals the controller. In response, thecontroller enables the power source which delivers power to the two-waytransmission line.

This approach is useful for detecting a short in the two-waytransmission line. For example, if the detector output was shorted tothe detector return, both the first and the second group of test pulseswould be detected by the detector. This information would be signaled tothe controller. The controller would process the results concluding thata short in the two-way transmission line has occurred since both thefirst and second group of test pulses were received. In response, thecontroller would not enable the power source.

FIG. 4 shows a detecting station 10 subsection and a DTE requiring power20′. The detecting station includes logic 100, transmitter 102, receiver104, a detector transmit transformer 106, a detector receive transformer108, and a power source 110. The DTE includes DTE circuitry 120, areceiver 126, a transmitter 124, a DTE receive transformer 116, a DTEtransmit transformer 118, a relay 112, and a filter 34.

The test pulses are generated by the logic 100 and coupled to thetransmitter 102. The output of the transmitter is coupled to the primarywinding of the transmit transformer causing the test pulses to beinduced into the secondary winding. The secondary winding of thetransmit transformer is coupled to a DTE power source. The power sourceis isolated from the transmitter and receiver to protect theircircuitry. The test pulses from the secondary winding of the transmitterare transmitted to the DTE. The wires between the detecting station andthe DTE requiring power are shown in FIG. 5 between the dashed lines122. The test pulses do not energize the relay 112 because the testpulses are AC. The test pulses transmitted to the secondary windings ofthe DTE transformer are indirect to the primary side of the DTE receivetransformer 116.

In the absence of power in the DTE, the test pulses on transformers 116,112 are directed through the low-pass filter 84. The primary winding ofthe DTE receive transformer 116 is coupled to the primary winding of theDTE transmit transformer 118 through a low-pass filter 34. The testpulses from the DTE receive transformer 116 are directed through filter34 to the primary winding of the DTE transmit transformer 118. The testpulses are from the primary winding of the DTE transmit transformer areinduced into the secondary winding of the DTE transmit transformer 118.The condition of the absence of the power on the DTE, the receive signalpassing through the filter to the transmitter side of the DTE isreferred to as the loopback condition. The induced test pulses from thesecondary winding of the DTE transmit transformer sends pulses on thedetector return line. The test pulses on the detector return are coupledto the secondary winding of the detector receive transformer 108,thereby inducing the test pulses into the primary winding of thereceiver 104.

The logic 100 compares the test pulses sent with the test pulsesreceived. If the test pulses match, then a DTE requiring power has beendetected. Once the DTE requiring power is detected, the detectorsupplies power via the transmission line to the DTE requiring power. Thepower is directed from a power supply 110 of the detector to thedetector output onto the transmission wires. The DTE power sink absorbsthe power and the DC power activates the relay 112, thereby closing theswitches from the transformers 116, 118 and connecting the detector withthe DTE. The power connection to the DTE requiring power 20′ is comingfrom the detector output of the transformer as opposed to the detectorside of the DTE requiring power.

The power source may have a current limitation in order to preventhazards in case of a cable short while the detector is powered. Thetransformers 106, 108, 116, 118 provide isolation between the detector10 and the DTE requiring power 20′.

FIG. 5 shows the logic 100 that generates the test pulses and comparesthe test pulses with the received pulses. A word generator 84 is coupledto a register 82. The word generator 84 generates the test pulses whichin the prescribed exemplary embodiment is a 16-bit word. In thepreferred embodiment, the word generator 84 generates a pseudo-randomcode word. Alternatively, the word generator 84 is designed to generatea unique identifier, which can be a controller identifier. Theuniqueness of the word generator output, also referred to as the uniquecode word, increases the probability of correctly detecting a DTErequiring power through the loopback connection. The controllerinitiates the detection mode by generating an Initiate Detection trigger80, which causes the register 82 to latch the output of the wordgenerator 84. The register 82 is coupled to a pulse shaping device suchas a digital-to-analog converter (DAC) 86. The DAC is used to shape thepulse. In the preferred embodiment, the DAC generates a link pulse shapein accordance with IEEE 802.3u and IEEE 8802.3 The digital-to-analogconverter (DAC) 86 converts the test pulses into analog signals foroutput to the DTE. The controller indicates the length of the testpulses by writing to register 90. Register 90 determines the length ofthe test pulses by being coupled to the DAC. In the preferredembodiment, in accordance with IEEE 802.3u and IEEE 8802.3, the typicaltest pulse is 100 ns wide. By programming register 90, the test pulsewidth can be widened, such as 20 us or more.

A signal detecting device such as an analog-to-digital converter (ADC)converts the DTE output analog signals to digital signals. The ADC iscoupled to a register 93. The register 93 is coupled to a comparator 94and latches the ADC output for use by the comparator 94.

The window time period is programmable. The controller programs the timewindow by writing to the programmable register 91. Register 91determines the length of the time window by being coupled to timer 92.The timer 92 enables comparing 94 the sent test pulses with the receivedtest pulses for the window time period. If the sent test pulses are thesame as the received pulses and the received pulses within the windowtime, then the comparator indicates a match 95. If the received pulsesare not the same as the sent pulses or are not received within thewindow time, then the comparator indicates a mismatch 97. The purpose ofthe window time period is to improve the probability of correctlymatching sent test pulses with received test pulses and reduce theprobability of mis-detecting another detector sending the same uniquecode word.

The logic 100 is controlled via the flow/state diagram in FIGS. 7 and 8for the basic and preferred embodiments, respectively. In the preferredembodiment, flow/state diagram is embedded within the IEEE standard802.3u clause 28 auto-negotiation definition and inter-operates with allthe devices designed to that standard.

In addition to configuring the detector to transmit two groups of testpulses, it is also desirable in certain embodiments of the presentinvention to implement the power source with current limiting capabilityin the event of a short circuit in the two-way transmission line.

An exemplary embodiment of the low-pass filter is shown FIG. 6. Thelow-pass filter is a 3-pole filter with a cutoff frequency of 880 kHz.In the described exemplary embodiment, the low pass filter comprises a7.0 uH inductor 128, two 2 nF capacitors connected in parallel 130, 132,and a zero ohm resistor 134. The zero ohm resistor is a placeholder toshow that the values of the inductor, capacitors, and resistor can havedifferent values, such that the cutoff frequency is 880 kHz.Alternatively, the low pass filter can have any cutoff frequency thatpasses low frequencies.

The detector provides support for identifying data terminal equipmentcapable of accepting power via media dependent interface. Such a DTE istypically connected to a Ethernet switch capable of detecting itspresence and able to establish signaling with it. The process ofidentifying DTE power via MDI capable is termed DPM. The detectorprovides support for an internet-protocol based telephone, known as IPPHONE. The IP PHONE is one type of DTE.

The detector is capable of normal Auto-Negotiation, which is its defaultstate, or a modified Auto-Negotiation when its DPM detection mode isenabled. The Auto-Negotiation scheme is embedded within the IEEE 802.3uClause-28 rules. Therefore, the detector can be connected to either anIP PHONE or a non-IP PHONE without detriment to the detector operation.

When the detector starts Auto-Negotiation and DPM detection is enabled,it sends a unique Fast Link Pulse (FLP) word that is different from aformal FLP word. If the Link partner is DPM capable, it returns thisunique FLP word. Otherwise, the detector may receive the Link partner'sword instead of the unique FLP word sent. The detector updates aregister containing relevant status bits that the controller (Control)can read. The detector continues to send the unique FLP word if noresponse is received from the Link partner. The controller, at any time,can disable DPM detection and restart Auto-Negotiation to establishnormal link with the Link partner.

Upon power-up the detector defaults to normal mode, non-DPM detectionmode, as per the IEEE 802.3u standard. The detector includes a shadowregister, DPM, containing required ‘enable’ and ‘status’ bits for DPMsupport.

If the DPM detection mode is enabled, through modifications to theAuto-Negotiation algorithm, the detector sends a unique Fast Link Pulse(FLP) word that is different from a normal FLP word. If the Link partneris a DPM, this unique FLP word externally loops back to the device.Otherwise, the device may receive the Link partner's word instead of itsown unique FLP word. The detector is capable of robustly determining ifits partner is DTE type or not. Upon determination, the detector updatesa register containing relevant status bits that the controller can read.The detector continues to send the unique FLP word if no response isreceived form a partner. The controller, at any time, can disable theDPM detection mode and restart the Auto-Negotiation to establish normallink with a Link partner.

FIG. 7 shows the sequence for DPM detection combined withAuto-Negotiation in a basic embodiment of the invention. Table 1 and 2show DPM register bits and their description. DPM detection can be resetor restarted along with auto-negotiation or link loss 160. Thecontroller can enable DPM detection by setting the DPMDETEN bit to a “1”and restart Auto-Negotiation by setting ANRSTRT bit to a “1” 162. Ifthese bits are not set, then normal auto-negotiation proceeds 164. Whenthe DPM detection mode is enabled, the device loads an internallygenerated unique (random) word into the Auto-Negotiation Advertisementregister, also called an FLP register 166, and begins to transmit thisFLP word 168. In the basic embodiment, while this word is transmitted,link pulses' width can be increased from a normal 100 ns to 150 ns ifLPXTND bit is set to a “1”. In the preferred embodiment, while this wordis transmitted, the link pulse width can be increased from 150 ns to 950ns, in 100 ns increment per FLPWIDTH register, if LPXTND bit is set to a“1”. If LPXTND bit is a “0” then a default link pulse width of 100 ns isused. The wider link pulse enhances the cable reach for the DTE if theexternal loopback is over CAT 3 cabling.

In the basic embodiment, if the unique FLP word is not received from theLink partner, then the detector continues to send the DPM FLP burst 170.If the unique FLP word is received from the Link partner 172, then thedetector checks if the sent FLP burst matches the received FLP burst174. If they match, then the detector sets its DPMSTAT bit to a “1” 176.The received unique FLP word indicates a DPM detection. If it receivesany other FLP word, the detector sets its MISMTCH bit to a “1” 178,indicating a non-DPM detection. After it sets either the DPMSTAT orMISMTCH bit, the detector stops auto-negotiation and waits in theTX-Disable state of the Auto-Negotiation arbitrator state machine. Thecontroller polls the mutually exclusive DPMSTAT and MISMTCH bits, todetermine if a partner is detected and if the partner is DPM capable. Ifthe partner is a DPM capable, the power to the DTE is supplied throughthe UTP cable. After the partner has been identified through the DPMSTATor MISMTCH bit, to establish link with the partner, the DPMDETEN bitshould be disabled, and Auto-Negotiation process restarted.

In the preferred embodiment, DPM detection can be reset or restartedalong with auto-negotiation or link loss 180. The controller can enableDPM detection by setting the DPMDETEN bit to a “1” and restartAuto-Negotiation by setting ANRSTRT bit to a “1” 182. If these bits arenot set, then normal auto-negotiation proceeds 184 and the MISMTCH bitis set to “1” and the DPMSTAT bit is set to “0” 86. When the DPMdetection mode is enabled, the device loads an internally generatedunique (random) word into the Auto-Negotiation Advertisement register,also called an FLP register 188, and begins to transmit this DPM FLPword 190. In the preferred embodiment of the invention, the detectorcontinues to send out an internally generated unique DPM FLP word, FLPburst, during the DPMDETEN mode, until the detector detects energy fromthe Link partner 192.

In the preferred embodiment, when the detector detects energy from theLink partner, the detector takes the checks if an FLP word has beenreceived 194. If no FLP is received, then the detector starts andcompletes parallel detection 196, sets MISMTCH bit to a “1”, setsDPMSTAT to “0” 198, and enters link phase as per the parallel detection.The detector then check whether the received FLP matches the DPMFLP.100. If the received FLP word does not match the DPM FLP burst thenthe detector sets MISMTCH bit to a “1”, sets DPMSTAT to “0” 198, andcompletes Auto-Negotiation and enters link phase. If the received FLPword matches the DPM FLP burst then the detector sets DPMSTAT bit to a“1” 202. The detector checks if the DPMCONT bit is set to “1” 204. IfDPMCONT bit is a “0” then the sytem stops Auto-Negotiation 206 and waitsfor the controller before taking further action. If DPMCONT bit is a “1”then the detector sends a DPM FLP burst 208 and monitors the state ofreceive FLP timer and energy from the Link partner.

The detector checks whether the Max FLP Receive timer expired 210. Ifthe Receive FLP timer has expired, then the detector sets the DPMSTATbit to a “0” 212 and starts over the DPM detection.

If the Receive FLP time has not expired, then the detector checks ifenergy is detected 214. If energy is not detected, then the detectorchecks if the FLP receive time expired. If energy is detected, then thedetector checks whether the FLP has been received 216. If energy isdetected from the Link partner but no FLP is received then the sytemstarts and completes parallel detection, sets MISMTCH bit to a “1”, setsDPMSTAT to “0”, and enters link phase as per the parallel detection 196.If an FLP is received, then the detector checks whether the received FLPmatches the DPM FLP burst 118. If energy detected from the Link partneris an FLP word and if it matches the DPM FLP burst then the detectorreturns to sending a DPM FLP burst 108. If energy detected from the Linkpartner is an FLP word but it does not match the DPM FLP burst then thesytem sets MISMTCH bit to a “1”, sets DMPSTAT to “0” 86 and completesAuto-Negotiation and enters link phase.

Table 1 gives a bit summary of the register, 0Fh (15 decimal), in thebasic embodiment of the invention. The register, 0Fh (15 decimal), isconsidered a shadow register, and is referred to as a DPM register. Toaccess the shadow register, the “Spare Control Enable”, bit 7, ofregister 1Fh must be set. TABLE 1 DPM Register summary ADDR NAME 15-5 43 2 1 0 DEFAULT OFh DPM Reserved LPXTND MISMTCH DPMSTAT ANRSTR DPMDETEN0000h (15d)

Table 2 shows a detailed description of the DPM register bits in thebasic embodiment of the invention. TABLE 2 DPM REGISTER (ADDRESS OFH, 15D) BIT NAME R/W DESCRIPTION DEFAULT 15-6 Reserved RO Write as “0”,Ignore when read 0 5 DPMWINEN R/W 0 Windowing scheme enable to reduce ipmis- detection probability 4 LPXTND: Extend Link Pulse width R/W 0 =Normal link pulse width (100 ns) 4 1 = Set Link pulse width to 150 ns 3MISMTCH: Word Miss match RO 1 = Fast Link Pulse Word miss match occurred0 during DPM detection 2 DPMSTAT: Status RO 1 = Link partner is DPMcapable 0 1 ANRSTRT: Restart R/W 1 = Restart Auto-Negotiation (identicalto Reg. 0 0 bit 9) but used for DPM detection 0 DPMDETEN: DPM enable R/W1 = Enable DPM detection mode 0

LPXTND is Extend Link Pulse width. When this bit is set to a “1”, thesystem increases the FLP width from a normal 100 ns to 150 ns.

MISMTCH is Word Mismatch. When DPM detection is enabled, the Linkpartner's FLP word is compared to the unique FLP word sent. MISMTCH bitis set to a “1” if the comparison fails indicating that the Link Partneris not DPM capable. MISMTCH bit is set to “1” for detecting any legacyEthernet device: either Auto-Negotiation or forced to 10 or 100 Mbitsspeed.

DPMSTAT is DPM Status, When DPM detection is enabled, the Link partner'sFLP word is compared to the unique FLP word sent. If it matches, theLink Partner is DPM capable and DPMSTAT bit is set to a “1”.

ANRSTRT is Restart. This bit, when set to a “1”, restarts theAuto-Negotiation. The detector, after power up, is in a non-DPMdetection mode. If DPM detection is needed DPMDETEN bit should be set toa “1” and restart the Auto-Negotiation. Auto-Negotiation can also berestarted by setting bit 9 of reg. 0 (Control Register) to a “1”.

DPMDETEN is DPM detection mode. When this bit is set to a “1”, thedetector enables DPM detection when Auto-Negotiation is re-started.Otherwise, the system Auto-Negotiates in a non-DPM detection mode as perthe IEEE 802.3u standard. When in DPMDETEN mode, if a legacy Ethernetdevice is detected through either normal Auto-Negotiation Ability Detector Parallel Detect paths, the Negotiation process continues to acompletion, where link between the two stations is established.

Table 3 shows a detailed description of the MII register, 0Fh (15decimal), referred to as a DPM register and its bits definition in thepreferred embodiment of the invention. TABLE 3 DPM Register Summary(Address OFh, 15d)

OFh DPM FLPWIDTH Reserved DPMCONT Reserved LPXTND MISMTCH DPMSTAT ANRSTRDPMDETEN 0000h (15d)

Table 4 shows a detailed description of the MII register, OFh (15decimal), referred to as a DPM register and its bits definition. TABLE 4DPM Register (Address OFh, 15 d)

15-11 FLPWIDTH[4:0} R/W FLP width increment register 0 10-7  Reserved ROWrite as “0”, Ignore when 0 read 6 DPMCONT R/W 0 = Stop after detectinga DPM 0 capable 5 Reserved RO Write as “0”, Ignore when 0 read 4 LPXTND:Extend R/W 0 = Normal link pulse width 0 Link Pulse width (100 ns) 1 =Set Link pulse width to 150 ns 3 MISMTCH: RO 1 = Fast Link Pulse Word 0Word mismatch mismatch occurred during DPM detection indicating that thelink partner is a legacy device 2 DPMSTAT: RO 1 = Link partner is DPM 0Status capable 1 ANRSTRT: R/W 1 = Restart Auto-Negotiation 0 Restart(identical to Reg. 0 bit 9) but used for DPM detection 0 DPMDETEN: R/W1 - Enable DPM detection 0 DPM enable mode

FLPWIDTH [4:0] is the FLP width in DPMDETEN mode. When the detector isin DPMDETEN mode, if LPEXTND is set for a “1” then the FLP pulse widthcan be changed from a default 100 ns to 150 ns. The width can be furtherincreased to a maximum of 950 ns in 100 ns increments as specified bythe FLPWIDTH, a 5 bits register. Although the FLP width can betheoretically increased to 150+31*100=3250 ns, due to TX magneticcharacteristics, it is not recommended to increase the FLP width morethan 950 ns.

DPMCONT is Continuous DPM Detect Enable. While in DPMDETEN mode if thisbit is set to a “1”, after initially detecting a DPM capable Linkpartner, the detector continues to monitor the presence of a DPM capableLink Partner. While in this continuous DPM detection mode, if it detectsa non DPM Link partner, the detector establishes a link with the Linkpartner if possible. FIG. 7 shows the details of the DPM detectionprocedure combined with Auto-Negotiation.

LPXTND is Extend Link Pulse width. When this bit is set for a “1”, thedetector increases the link pulse width from a normal 100 ns to 150 ns.Additionally, the link pulse width can be increased to a maximum of 950ns to 100 ns increments per register FLPWIDTH.

MISMTCH is Word Mismatch. When DPM detection is enabled, the Linkpartner's FLP word is compared to the unique FLP word sent. MISMTCH bitis set for a “1” if the comparison fails indicating that the LinkPartner is not DPM capable.

DPMSTAT is DPM Status. When DPM detection is enabled, the Link partner'sFLP word is compared to the unique FLP word sent. If it matches, theLink Partner is DPM capable and DPMSTAT bit is set to a “1”.

ANRSTRT is Restart. This bit, when set to a “1”, restarts theAuto-Negotiation. The detector, after power up, is in a non-DPMdetection mode. If DPM detection is needed DPMDETEN bit should be set toa “1” and restart the Auto-Negotiation. Auto-Negotiation can also berestarted by setting bit 9 of reg. 0 (Control Register) to a “1”.

DPMDETEN is DPM detection enable. When this bit is set to a “1”, thedetector enables DPM detection when Auto-Negotiation is restartedOtherwise, the detector Auto-Negotiates in a non-DPM detection mode asper the IEEE 802 3u standard.

In addition to DPM detection, the detector is capable of generatinginterrupts to indicate DPMSTAT bit change if interrupt mode is enabled.The detector has a maskable interrupt bit in the MII register 1Ah. Bit12, DPMMASK of register 1Ah, when set to a “1” disables generation ofDPMSTST change interrupt. Bit 5, DPMINT, of register 1Ah indicates thatthere has been a change in DPMSTAT bit. TABLE 5 Interrupt Register(Address 1Ah, 26d)

1Ah INTERRUPT Reserved DPMMASK Reserved DPMINT Reserved 9F0Xh

DPMINT is: DPM Interrupt. Bit 5 of MII register 1Ah, a read only bit, ifread as a “1”, indicates that there has been a DPMSTAT bit change in theDPM detection process. The change indicated could be from a “0” to a “1”or from a “1” to a “0”. Additionally, if interrupt has been enabled andDPMMASK is a “0”, then the detector generates an interrupt. Reading ofregister 1Ah clears DPMINT bit and interrupt that was caused by DPMSTATbit change.

DPMMASK is DPM Mask. When the detector is in DPMDETEN mode, bit 12 ofMII register 1Ah, when set to a “1” disables any interrupt generated bythe DPMSTAT change if interrupt is enabled. However, bit 5, DPMINT,provides a DPMSTAT change regardless of DPMMASK bit.

The FIG. 7 flowchart shows the sequence for DPM detection combined withAuto-Negotiation in a basic embodiment of the invention. The FIG. 8flowchart shows the sequence for DPM detection combined withAuto-Negotiation in a preferred embodiment of the invention.

The following items highlight enhancements made in the preferredembodiment of the invention.

Link pulse width. In DPMDETEN mode if LPXTND bit is set to a “1”, theFLP width is changed from a normal 100 ns to 150 ns. In addition tothis, the detector can increase this width in 100 ns increments, asspecified by the FLPWIDTH register. A value of “00000”b (default) in theFLPWIDTH register would be equivalent to the basic embodiment of theinvention.

In the basic embodiment of the invention, if MISMTCH bit is set to a “1”while LPXTND bit is a “1”, then the link pulse width remains at 150 nsduring normal Auto-Negotiation phase. In the preferred embodiment of theinvention, the link pulse width is switched back to 100 ns during normalAuto-Negotiation phase.

Continuous DPM detection. The preferred embodiment of the inventionincorporates an additional bit DPMCONT. While in DPMDETEN mode if thisbit is set to a “1”, after initially detecting a DPM capable Linkpartner, the detector continues to monitor the presence of a DPM capableLink partner. While in this continuous DPM detection mode, if it detectsa non-DPM Link partner, the detector establishes a Link partner ifpossible. FIG. 8 shows the details. In the preferred embodiment, the DPMdetection function is identical to the basic embodiment if DPMCONT bitis a “0” (default).

Interrupt. The preferred embodiment provides a maskable interrupt forthe DPMSTAT bit change. This is enabled by setting DPMMASK, bit 12 ofMII register 1Ah, to a “0” if the detector's interrupt bit 14 of MIIregister 1Ah is set for a “1”. In the preferred embodiment, if DPMMASKis set to a “1” (default) then the detector does not provide DPMSTAT bitchange interrupt as is the case in the basic embodiment.

DPM Detection Operation

The DPM detection process prevents the detector from supplying power toa legacy DTE not equipped to handle power through the MDI. In case thefar-end device is not a DTE requiring power, the far-end unit's linkdetection is unaffected by the DPM detection mechanism. The standardAuto-Negotiation process occurs in parallel to the DPM detectionprocess, enabling detection of non-DTE requiring power devices while DPMdetection is enabled. Randomization in the DPM detection algorithmprevents two detection-enabled stations from simultaneously applyingpower. The DPM detection scheme works over CAT-3, CAT-5, or bettercabling The detector is set to a mode to search for a DTE requiringpower. The DTE requiring power's RD pair is effectively connected to theTD pair through a low pass filter. The detector of the detecting stationtransmits a random code of sufficient uniqueness. The DTE requiringpower is detected through the detector of the detecting stationreceiving its unique random code through the DTE requiring powerloopback. Once the detecting station detects the presence of the DTErequiring power, it supplies detector power to the DTE requiring powervia an MDI connection.

The detecting station then performs an Auto-Negotiation with thenow-powered DTE requiring power. During the detection process, if thedetecting station receives valid 10Base-T NLPs, 100Base-TX idles, orAuto-Negotiation FLP code-words, it Auto-Negotiates normally.

To prevent a legacy link partner from saturating the detector's portwith valid packets when connected to a DTE requiring power without power(DTE requiring power loopback condition), the DTE requiring powerreceive pair (RD) is effectively connected to its transmit pair (TD)through a low pass filter. This low pass filter cuts-off the legacy linkpartner's valid data, avoiding network activity. The random code signalused for DTE requiring power detection must be of sufficiently lowfrequency content to pass through the filter, as well as two worst-caseCAT-3 cables. Once the DTE requiring power is applied, the DTE requiringpower loopback condition and low pass filter connection are removed andthe RD and TD pairs operate normally.

Following reset, the DPM Detection Mode (DPMDETEN) is disabled andnormal, IEEE Standard, Auto-Negotiation process begins. To enable theDPMDETEN mode, firmware must set the DPM Detection Enable bit, DPMDETEN(DPMFON reg, bit 0) to a ‘1’, and then set the Auto-Negotiation Restartbit, ANRSTRT (DPM reg, bit 1) to a ‘1’.

When in the DPMDETEN mode, setting the ANRSTRT bit causes a randomsequence to be loaded into the Auto-Negotiation Advertisement Transmitregister, and the first FLP word transmitted contains this sequence.While this sequence is transmitted, the link pulses are extended to 1.5times normal pulse width.

While in the DPMDETEN mode, as long as nothing is received from a linkpartner, the device continues to transmit the above FLP word. Once alink partner FLP burst is received, if it does not match the FLP wordfrom the device, then the link partner is not DPM capable. In this case,the device sets the DPM Mismatched bit, MISMTCH, (DPM reg, bit 3) to a‘1’.

If the link partner FLP burst received matches the FLP word the devicetransmitted, it indicates that the device at the other end is a DPM andits relay is closed to loopback the devices transmit data to its receiveport. In this case, the device sets the DPM Status bit, DPMSTAT, (DPMreg, bit 2).

In either case of detecting a DPM or a normal link partner, the devicestops the Auto-Negotiation process and waits in the TX-Disable state ofthe Auto-Negotiation Arbitrator State Machine. The firmware must takethe necessary actions, e.g. power up the DPM, and then in either case,disable the DPMDETEN bit and Restart Auto-Negotiation to establish linkwith the partner.

The DPM register contains both the DPMSTAT and MISMTCH bits. Therefore,polling this register alone provides the necessary status information toindicate either a DPM or a normal link partner.

Firmware and DPM Detection Handshake

The detector is in normal Auto-Negotiation mode upon startup. TheFirmware enables the DPMDETEN mode (DPMDETEN bit) and sets the ANRSTRTbit. The detector sends out the DPM random sequence FLP word. Whilesearching for a DPM, if the received FLP burst matches what the detectortransmitted, then the remote partner is a DPM. The DPMSTAT bit is setand the Auto-Negotiation process is stopped.

On the other hand, while searching for a DPM, if a mismatch between thetransmitted and received FLP words occurs, then the remote device is nota DPM. The MISMTCH bit is set and the Auto-Negotiation process isstopped.

The firmware monitors the DPMSTAT and MISMTCH bits. Once either of thesemutually exclusive status bit is set, the firmware clears the DPMDETENbit and sets the ANRSTRT bit to complete the normal Auto-Negotiationprocess in order to link up with either the remote DPM or normal linkpartner.

DPM Mis-Detection Probability

It is possible that the device at the other end also attempts to searchof an DPM device using the same DPM Phone Detection procedure. If thelink partner is another embodiment of the invention (another systemdetector), then the chances of both devices sending out an identical FLPword is 1 in 2¹⁴.

To further reduce the mis-detection probability, the detector includes atime windowing scheme. If a matching FLP burst is received within themaximum time allowed for the FLP burst to make a round trip back to itsreceive port, the DPMSTAT bit is set. In the preferred embodiment, thismaximum time is set to 16 us, which is more than the actual maximumround trip time for the longest cable length The maximum time isprogramable. Since a device can send out an FLP burst at any time withina 16 ms window, the probability of it sending out the FLP burst in any16 us span is 1 in 1000. Therefore, the mis-detection probability is 1in (2¹⁴ multiplied by 1000), or 1 in 16 million events.

When mis-detection does happen, one or both devices erroneously sets theIPSTAT bit. It's then up to the firmware to monitor this mis-detectionevent and take the appropriate actions.

Although a preferred embodiment of the present invention has beendescribed, it should not be construed to limit the scope of the appendedclaims. For example, the present invention can be implemented by both asoftware embodiment or a hardware embodiment. Those skilled in the artwill understand that various modifications may be made to the describedembodiment. Moreover, to those skilled in the various arts, theinvention itself herein will suggest solutions to other tasks andadaptations for other applications. It is therefore desired that thepresent embodiments be considered in all respects as illustrative andnot restrictive, reference being made to the appended claims rather thanthe foregoing description to indicate the scope of the invention.

1-53. (canceled)
 54. A method of detecting whether a data terminalequipment device (DTE) is receiving power, comprising: transmitting atest signal over a two-way data transmission line to a DTE; receiving aresponse signal from the DTE via the two-way data transmission line;determining, based on the response signal, whether the DTE is receivingpower; and if it is determined that the DTE is not receiving power,operatively coupling a power source to the two-way data transmissionline to provide operating power to the DTE.
 55. The method of claim 54,wherein determining, based on the response signal, whether the DTE isreceiving power comprises determining that the DTE is receiving power ifthe response signal comprises the test signal.
 56. The method of claim54, wherein the response signal comprises at least a portion of the testsignal.
 57. The method of claim 54, wherein receiving a response signalfrom the DTE via the two-way data transmission line comprises receivingthe test signal from the DTE.
 58. The method of claim 54, wherein theDTE comprises an IP phone.
 59. The method of claim 54, wherein the stepof operatively coupling the power source to the two-way datatransmission line occurs only if the response signal comprises the testsignal.
 60. The method of claim 54, wherein the test signal comprises atleast a first pulse characterized by a first pulse width and a secondpulse characterized by a second pulse width that is substantiallydifferent from the first pulse width.
 61. A power detection system fordetecting whether a coupled device is not receiving power from a powersource, comprising: a first device that transmits a signal to thecoupled device over a two-way data transmission line; and a seconddevice that causes operating power to be supplied over the two-way datatransmission line if the first device receives the signal from thetwo-way data transmission line.
 62. The power detection system of claim61, wherein the first device comprises a physical layer transceiver, andthe second device comprises a controller.
 63. The power detection systemof claim 61, wherein the signal comprises a predetermined test signal.64. The power detection system of claim 61, wherein the signal comprisesa random word.
 65. The power detection system of claim 61, wherein thecoupled device comprises a data terminal equipment device.
 66. A methodof detecting a data terminal equipment device (DTE) that is notreceiving power, comprising: determining whether a DTE coupled to atwo-way data transmission line is receiving power; and providing powerto the DTE via the two-way data transmission line if it is determinedthat the DTE is not receiving power.
 67. The method of claim 66, whereindetermining whether a DTE coupled to a two-way data transmission line ifreceiving power comprises transmitting a signal to the DTE anddetermining whether the signal returns from the DTE.
 68. The method ofclaim 66, wherein determining whether a DTE coupled to a two-way datatransmission line is receiving power comprises transmitting a testsignal to the DTE and determining whether a first portion and a secondportion of the test signal returns from the DTE.
 69. The method of claim66, wherein the DTE comprises an IP phone.
 70. The method of claim 66,further comprising detecting whether the DTE is coupled to the two-waydata transmission line.
 71. A power detection system comprising: a firstdevice that determines, using a test signal, whether a data terminalequipment device (DTE) coupled to a two-way data transmission line isreceiving power; and a second device that causes a power source to becoupled to the two-way data transmission line for providing operatingpower to the DTE if it is determined that the DTE is not receivingpower.
 72. The power detection system of claim 71, wherein the firstdevice determines whether the DTE is receiving power by, at least inpart, transmitting a signal to the DTE and determining whether thesignal returns from the DTE.
 73. The power detection system of claim 71,wherein the first device determines whether the DTE coupled to thetwo-way data transmission line is receiving power by, at least in part,transmitting a test signal to the DTE and determining whether a firstportion and a second portion of the test signal returns from the DTE.74. The power detection system of claim 71, wherein the DTE comprises anIP phone.
 75. The power detection system of claim 71, wherein the firstdevice further determines whether the DTE is coupled to the two-way datatransmission line.
 76. A method for detecting whether a device isreceiving power from a source other than over a transmission line,comprising: transmitting a pulse to the device over a transmission line;receiving the pulse from the device over the transmission line; anddetermining whether the device is receiving power from a source otherthan over the transmission line in response to at least the receivedpulse.
 77. The method of claim 76, further comprising determiningwhether the device is receiving power in response to at least thereceived pulse.
 78. The method of claim 76, further comprising:transmitting a second pulse to the device over a transmission line;receiving the second pulse from the device over the transmission line;and determining whether the device is receiving power from a sourceother than over the transmission line in response to at least thereceived second pulse.